Recently, new magnetic resonance examination system designs have been proposed, in which the main magnet system comprises magnet coils of superconductive material, and in which the magnetic field gradient system is located at the outside of the superconducting coil system and a weak-iron flux conduction system is provided to guide the magnetic gradient flux into the patient bore. A detailed description of such a magnetic resonance examination system is given in International Patent Application published as WO2005/124381 A2. A main advantage of such new magnetic resonance examination systems is a reduced scanner acoustic noise (“silent imaging”). Furthermore, the superconductive coils of the main magnet are closer to the examination region without compromising the effective bore size. Accordingly, less superconductive material is needed, which reduces the overall costs of the magnetic resonance examination system.
From conventional magnetic resonance examination systems, it is known to use a balanced bridge circuit to detect emerging quenches, i.e. loss of superconducting state in part of the coil. However, the arrangement of the magnetic field gradient system outside of the main magnet of the magnetic resonance examination system may induce voltages in the main magnet, which could misleadingly be interpreted as a quench. Prior art quench detecting methods are therefore not suitable to ensure a reliable detection of a quench of the superconducting main magnet of such a magnetic resonance examination system.